The crown-of thorns starfish, Acanthaster planci, has been blamed for coral mortality in a large number of coral reef systems in the Indo-Pacific region. Because population outbreaks of A. planci are closely related to reproduction, it is important to examine the mechanism of reproductive control in this starfish. Previously, a relaxin-like gonad-stimulating peptide (RGP) in starfish Asterina pectinifera has been identified as the gonadotropin responsible for final gamete maturation. On the basis of homology research on RGP cDNAs from several species, this study was carried out to identify gonadotropin in A. planci. The cDNA sequence of RGP was determined using a RACE product of mRNA from the radial nerves of A. planci. The coding DNA sequence consisted of 351 base pairs with an open reading frame encoding a peptide of 116 amino acids (aa), including a signal peptide (29 aa), B-chain (19 aa), C-peptide (44 aa), and A-chain (24 aa). The chemical structure of A. planci RGP was exactly the same as that of A. pectinifera RGP. Furthermore, synthetic RGP could induce gamete spawning and oocyte maturation in the ovarian fragments of A. planci. This strongly suggested that the RGP is a gonadotropin in A. planci.
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